Power transistors, in particular power MOS transistors, such as power MOSFETs or power IGBTs, are widely used as electronic switches for switching electric loads, such as motors, actors, lamps, or the like. A power transistor is a voltage controlled device that can be controlled (switched on and off) by an electronic drive circuit configured to supply a drive signal to a control terminal (gate terminal) of the power transistor. The drive circuit may include at least one transistor.
A power transistor can be implemented to have a voltage blocking capability of several 100V. A voltage blocking capability of the at least one transistor of the drive circuit is usually selected such that this transistor is capable of withstanding a maximum signal level of the drive signal. This maximum signal level is, for example several 10V, such as about 20V. Thus, the at least one transistor of the drive circuit can be implemented with a much lower voltage blocking capability than the power transistor.
Power MOS transistors include a gate electrode that is operable to control a conducting channel in a body region of the transistor, and that is dielectrically insulated from the body region by a gate dielectric. Towards the end of a transistor manufacturing process it is desirable to test the gate dielectric for defects, wherein those MOS transistors that have a defective gate dielectric are discarded. Testing the gate dielectric may include applying a test voltage between the gate electrode and the body region and measuring a current through the gate dielectric. A MOS transistor may be discarded when the current is higher than a predefined threshold. The testing voltage is higher than the maximum signal level of the drive signal in a normal operation. For example, the testing voltage is between two times and five times the maximum signal level of the drive signal.
In order to save costs and in order to save space it is desirable, to integrate the power transistor and the driver circuit in the same semiconductor body. However the high voltages applied to the gate electrode of the power MOS transistor during the testing of the gate dielectric may destroy the at least one transistor of the drive circuit, if this transistor is not designed with a sufficiently high voltage blocking capability. However, a high voltage blocking capability of this transistor is usually associated with a high on-resistance and, therefore, with high driving losses.
There is therefore a need to provide an integrated circuit with a power transistor and a driver circuit integrated in a common semiconductor body, wherein the driver circuit can be implemented with at least one driver transistor having a relatively low voltage blocking capability.